This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Voltage-dependent potassium channels (Kv) control the flow of K+ through the cell membrane in response to changes in membrane potential. The opening of Kv channels causes membrane hyperpolarization that can curtail excessive membrane excitability or simply tone down normal membrane activity. Kv channels are central to many fundamental biological processes, such as nerve conduction, muscle contraction, and hormone secretion. In a cell, Kv channels are always associated with many other proteins to form a macromolecular complex, and the associated proteins modulate channel functions. The long-term goal of our research is to develop an atomic level understanding of channel modulation mechanisms. In this project, we focus on modulation of Kv channel by beta subunit. We have found that beta subunit is an oxidoreductase that utilizes an NADPH cofactor to catalyze a redox reaction. We also found that beta subunit bound with an NADPH (reduced) or an NADP+ (oxidized) modulates channel function differently. We will solve high resolution structures of the beta subunit in complex with intracellular channel domains, in reduced and in oxidized forms. We will also solve structure of the beta subunit in complex with small molecule modulators that affect channel functions.